This is a King 6m Conversions Heathkit SB-220 I repaired for a friend. It just stopped working mid-stream...Plate current dropped to 0, not even idle current. Plate voltage was good, t/r relay working, etc. Instead of a Zener, it uses a string of series connected diodes, allowing "fine tuning" of the bias. I found the solder had melted from the joints on the pcb, and caused lots of bad connections. I replaced the diodes, cleaned the old solder, and resoldered them. All was well and it was up and running. Here's a few pics...
